Metallic mold and process of forming the same



Patented Sept. 16, 1930 NITED STATES LYESJM PATENT; o'FFicE WILLIAM H. SMITH, OF DETROIT, MICHIGAN No Drawing.

This invention relates to metallic molds and process of forming the same, and has to do particularly with the materials for and process of forming metallic molds for hot metal casting.

Molds of the metallic permanent type, known generally as permanent molds, are Well known in the art'and have heretofore, been formed of machined cast metal or from machined castings of various shapes.

Many attempts have been made to improve the art of permanent mold casting by providing various materials for impregnating or coating the mold faces, and other attempts toward improvement in this art have included varying the structure of the mold walls to affect heat control in the casting and cooling operations.

It is the object of the present invention to provide metallic molds the walls of which are formed of a material having a relatively higher melting point and a much greater resistance to heat transfer than that of the. ordinary grey iron. It is also the objectof the present invention to afford a process for combining and forming the materials going to make up the walls of the molds, and a novel manner of combining and forming said materials. More specifically, the materials forming the walls of my novel mold structure comprise finely divided iron such as is produced by the removing of oxygen from iron ore, leaving the element iron in the finely divided state, together with unreduced metallic oxides or similar material. The process relates to the compressing or sintering of the mold materials into a 1 mass.

The specific structure and contour of the metallic or permanent molds does not enter into the present invention and it will be understood that the molds embodying my invention may be of any type or shape as desired. a

In carrying out my invention I preferably utilize an iron which I term sponge iron which is an iron produced by the removing of oxygen from the iron ore without melting. Such a sponge iron may be pro- 50 duced by the method and apparatus disclosed Application filed April 22,

1927. Serial No. 185,909.

in my copending application Serial No. 88,774, of February 17, 1926. Such method and apparatus does not form a part of this invention and therefore does not here require illustration by drawings. It will be understood, however, that I do not limit myself to the use of sponge iron produced by the reduction of ore at relatively low temperatures; but that an iron may be utilized which has a porosity such as produced by the electrolytic decomposition of iron. In other words, I preferably utilize iron in a finely divided state or which is open in its atomic form, or what might be called atomically divided.

In carrying out my novel process the finely divided metallic iron or sponge iron is associated with unreduced metallic oxides in the proportions desired in accordance with the conductivity and melting point desired for the walls of the mold. Of course the finely divided iron or sponge iron may be directly compressed or sintered into a mass to form mold walls for the casting of the metals, as such finely divided iron has a relatively higher melting point and lower conductivity than grey iron or iron ore with combined elements. However, I prefer to associate metallic oxides, such as calcium or magnesium oxides, with the finely divided or reduced iron as such metallic oxides, which might be termed gangue will combine with the pure iron to greatly raise the melting point and lower the conductivity whereby molds or mold walls formed of such combined materials will present much greater resistance to heat transfer than if the molds were made from pure element iron or iron alloys.

The unreduced metallic oxides may be associated with the unreduced sponge iron or finely divided metallic iron at the time it is taken from the furnaces, or the metallic oxides or gangue may be mixed with the finely divided iron after the reduction process. If the metallic oxides are associated with the finely divided iron as taken from the furnace retorts, I preferably take this finely divided iron together with the associated gangue and while still comparatively cold, compress the same into the generally desired form or forms. The finely divided iron and gangue particles are thus held together by adhesion but not united. The heat resulting from the pressure applied to the mixture may conceivably be sufficient to cause sintering of the mass sufficient to form a uniform mass to make the mold Walls, and it is conceivable that the molten metal when poured in the molds would tend to further fuse the particles of finely divided iron and gangue at the first molding operation whereby the surfaces of the mold walls will be affected to greatly raise the melting point and increase the re sistance of heat transfer. However, in the practical carrying out of my process I prefer to compress the mixture while still comparatively cold and then place the roughly compressed mixture under a sintering temperature and in a reducing atmosphere. This reducing atmosphere may be obtained in any one of several ways, such as enclosing the compressing apparatus in atmosphere that is reducing and not oxidizing. Such apparatus would be obvious to one skilled in the art and does not form a part of the present in vention. When this mass of finely divided iron and gangue is sufficiently sintered or fused the whole massis then placed under pressure whereby to form a solid uniform mass, forming molds, or other forms to use in the forming of molds. The molds or mold walls are thus formed to present surfaces which are smooth and finished without the necessity of casting the metal and then machining the same. The finely divided iron together with the gangue having been sintered and compressed into a solid uniform mass thus presents walls having a relatively high melting point and being highly resistant to heat transfer. By forming molds or mold walls of such material I am able to cast grey iron or any other molten metals such as are now east in the art of die casting.

Heretofore grey iron has been cast in metal molds but the life of the molds has been very short and in most instances it has been necessary to coat or impregnate the faces of the mold cavities with various materials in order to resist the initial heat of the casting operation. With molds constructed of walls formed of the material as a result of my process it is not necessary to us coating materials of any kind as the materials formed as a result of my process have a melting point much higher than the molten grey iron or other metals or alloys and are much more highly resistant to heat transfer than grey iron molds, or even molds formed of pure iron or iron alloys.

I claim:

1. A method of forming permanent metallic mold walls, which comprises compressing a mass of finely divided iron having associated therewith a metallic oxide to increase the melting point of the compressed material, said finely divided iron and gangue being compressed to the desired form of mold walls without materially reducing the metallic oxide.

2. The method of forming permanent mold walls for casting metallic articles, which comprises associating metallic oxides with a mass of finely divided iron, bringing the mass to a sintering temperature, and placing said associated mass under pressure sufiicient to form a solid uniform mass without melting 01' materially reducing the oxides and a finished surface forming the wall or walls of the mold.

3. A method of forming the walls of permanent metallic molds, which comprises combining a mass of iron reduced without melting with a mass of finely divided ore, placing the combined mass under suflicient pressure to hold the mixture together, subjecting the compressed mass to a sintering temperature in a reducing atmosphere, then finally placing the sintered mass under a pressure suflicient to form the finished wall or walls of the mold Without melting.

4. A method of forming the walls of permanent metallic molds which comprises combining finely divided iron with metallic oxides, sintering the mixture into a mass and subjecting the sintered mass to pressure whereby to form and shape the wall or walls of the mold.

5. A method of forming the walls of permanent metallic molds, which comprises combining finely divided iron, such as sponge iron, with a gangue, compressing the mixture while comparatively cold into a mass, subjecting the mass to a sintering temperature in a non-oxidizing atmosphere and then subjecting the sintered mass to pressure whereby to form and shape the wall or walls of the mold.

6. As a new article of manufacture, a permanent metallic mold having mold walls formed of a mixture of sponge iron and a metallic oxide.

7 As a new article of manufacture, a permanent metallic mold having walls formed of a metallic mass, of finely divided particles of reduced iron and gangue held together by applied pressure Without melting.

8. As a new article of manufacture, a permanent metallic mold having mold Walls comprising a mixture of finely divided reduced iron and a metallic oxide, the prevailing material being finely divided iron.

9. As a new article of manufacture, a permanent metallic mold having Walls formed of a sintered mass of finely divided metallic particles and a predetermined amount of gangue held together by applied pressure without melting said predetermined amount of gangue serving to raise the melting point and lower the conductivity of the mass.

10. A heat exchange unit of the class described having Walls formed of a mixture of finely divided iron and a metallic oxide, the prevailing material being finely divided iron and the mixture being held together by applied pressure without melting, the proportion of metallic oxide in the mixture being predetermined to control the conductivity and melting point of the walls.

11. As a new article of manufacture, a metallic mold having walls formed of a mixture of finely divided reduced iron and one or more unreduced metallic oxides, said mixture being sintered and held together by applied pressure without melting.

In testimony whereof I aflix my signature.

WILLIAM H. SMITH. 

